Evidence for Ovarian Self-incompatibility as a Cause of Self-sterility in the Relictual Woody Angiosperm, Pseudowintera axillaris (Winteraceae)

Abstract

Species within the genus Pseudowintera exhibit high rates of self-sterility. Self-sterility in the genus has been previously posited-but not confirmed-to be the result of late-acting ovarian self-incompatibility (OSI) functioning within nucellar tissue of the ovule to prevent self pollen tubes from entering the embryo sac. Structural and functional aspects of pollen-carpel interactions and early seed development following cross- and self-pollination were investigated in P. axillaris to determine the site, timing and possible mechanisms of self-sterility. No significant differences were observed between pollen tube growth, ovule penetration and double fertilization following cross- and self-pollination. Pollen tubes exhibited phasic growth in an extracellular matrix composed of proteins and carbohydrates, as well as arabinogalactans/arabinogalactan proteins. A uniform failure in embryo sac development prior to division of the zygote was apparent within 15 d following double fertilization by self gametes. Results indicate that SI mechanisms in P. axillaris do not prevent double fertilization from occurring. Instead, mechanisms of self-sterility affect post-zygotic development of the embryo sac. Although self-sterility may be attributed to inbreeding depression, given the post-zygotic nature of failure in embryo sac development, the possibility of late-acting OSI is discussed.

Seed abortion in the sexual counterpart of Brachiaria brizantha apomicts (Poaceae)

“…This rejection process causes abortion of homozygous offspring during embryo development due to the presence of deleterious recessive alleles (Charlesworth and Charlesworth 1987;Matton et al 1994;Seavey and Carter 1996;Husband and Schenske 1996;De Nettancourt 1997). Early-acting inbreeding depression is generally characterized by: (1) a continuum of failure throughout the life cycle of the new generation and not by failure at a single stage; (2) variation in selfed individuals; (3) cross-compatibility among siblings or between progeny and parents due to the absence of SI genetic elements in the segregating alleles and (4) lack of success in embryo rescue due to the expression of homozygous lethal genes also under in vitro conditions (Seavey and Bawa 1986;Charlesworth and Charlesworth 1987;Husband and Schenske 1996;Sage and Sampson 2003). Since a gradual caryopsis rejection was observed in a continuum of developmental stages from 2 to 7 DAA, with the exception of 3 DAA, which was considered as an inconsistency, and since caryopses require 12 days to mature, seed abortion may be explained simply in the context of early-acting inbreeding depression.…”

Pollen viability, germination, and seed setting of Nelumbo nucifera

“…Cross-pollinated flowers of Bulnesia give a more than 35-fold higher seed-setting rate than self-pollinated flowers 39 . Crosspollination increases the rate of fertilization in Pseudowintera asillaris 42 . However, self-incompatibility partially limits seed set in Flourensia cernua 11 .…”

Self-sterility in the mutant ‘Zigui shatian’ pummelo (Citrus grandis Osbeck) is due to abnormal post-zygotic embryo development and not self-incompatibility

“…Bar (a,b,d,f-k,m-r) penetrate the embryo sacs (Kenrick et al 1986), or selfpollinated tubes could deposit sperm into the embryo sac but double fertilization was not achieved (Cope 1962). In addition, double fertilization in OSI can arrest division of zygotes after self-pollination (Sage and Sampson 2003;Bittencourt and Semir 2005). Post-zygotic OSI differs from inbreeding depression which is expected to cause embryonic failure during the different stages of development (Charlesworth 1985;Seavey and Bawa 1986).…”

“…There are about 20 species with LSI (Seavey and Bawa 1986) and 64 species exhibiting OSI (Gibbs and Bianchi 1999). Recently, species in families such as Solanaceae (Aguilar and Bernardello 2001), Bignoniaceae (Bittencourt et al 2003), Winteraceae (Sage and Sampson 2003), Bombacaceae (Gibbs et al 2004), and Brassicaceae (Primo and Machado 2009) have been reported to exhibit the LSI phenomenon. These results indicate that LSI exists extensively in many flowering plants.…”